Conventionally, a discharge lamp lighting circuit is structured such that, when an error occurs in the discharge lamp or in the circuit operation of the discharge lamp lighting circuit, the power supply to the discharge lamp is cut off by a protection circuit provided therein.
Conventionally, a discharge lamp lighting circuit which incorporates a protection function when an abnormal condition has occurred (for example, when an error in a load voltage or current due to the limited life of the discharge lamp is detected, that is, when the cause of an abnormal condition is considered to be permanent), the power supply to the discharge lamp is cut off. By contrast, when the cause of an abnormal condition is believed transient (for example, a transient variations in the power supply voltage or the like), the power supply to the discharge lamp is temporarily cut off but, thereafter, at the time when the cause for the abnormal condition disappears, the power supply to the discharge lamp is resumed.
However, when the abnormal condition cause is transient, if the power supply to the discharge lamp is cut off, then there is a concern that the resultant variations in the circuit condition (such as the lowered output voltage value and output current value of the lighting circuit) can be judged in error to be caused by a permanent abnormal condition.
For example, when the power supply to the discharge lamp is cut off temporarily due to a transient abnormal condition, the discharge lamp must be able to receive the supply of power again in the future when the cause of the transient abnormal condition disappears. However, if the protection circuit erroneously confirms that a secondary abnormal condition is produced due to the power supply cutoff condition, and also judges that the cause of the abnormal condition is a lasting or permanent cause, the supply of power to the discharge lamp will not be resumed.